Recently, lithium-ion batteries are used as rechargeable batteries in portable equipments, such as digital cameras. Because the lithium-ion battery is sensitive to overcharging and excessive discharging, the lithium-ion battery is used in the form of a battery pack including a protection circuit against overcharging and excessive discharging.
The battery pack may include a protection IC (Integrated Circuit). The protection IC may include an overcharge detection circuit, an excessive discharge detection circuit, an overcurrent detection circuit, and the like. The excessive discharge detection circuit turns OFF a switch within the battery pack when an excessive discharge is detected, in order to stop the discharge of the lithium-ion battery. The overcurrent detection circuit turns OFF a switch within the battery pack when an overcurrent is detected, in order to stop the discharge of the lithium-ion battery. The overcharge detection circuit turns OFF a switch within the battery pack when an overcharge is detected, in order to stop the charging of the lithium-ion battery.
In the overcharge detection circuit, the excessive discharge detection circuit, and the overcurrent detection circuit described above, the overcharge detection, the excessive discharge detection, and the overcurrent detection are determined and the corresponding switch is turned OFF when a corresponding detection time that is measured exceeds a predetermined time (delay time), in order to prevent an erroneous operation. In other words, it takes the predetermined time (delay time) for each of the overcharge detection, the excessive discharge detection, and the overcurrent detection to be determined.
However, when testing the protection IC at the time of fabrication, there is a problem in that the testing time will become long because it takes the predetermined time (delay time) to perform each of the overcharge detection, the excessive discharge detection, and the overcurrent detection. For this reason, when testing the protection IC, a short-test mode may be set to shorten the predetermined time (delay time) or, measures may be taken to eliminate the predetermined time (delay time).
For example, the Patent Document 1 proposes a circuit that judges whether an input level at a test terminal is a high level (VDD), a middle level (VDD/2), or a low level (VSS), and switches a delay time of a comparator output to one of a normal delay time mode, a short-delay time mode, and a no-delay time mode.